This invention relates to an optical illumination instrument, and more particularly an optical illumination instrument used in photolithographic process of manufacturing semiconductor devices.
FIG. 4 is a schematic diagram showing an assembly of an optical illumination instrument of prior art. A light source 41 comprising a mercury lamp or an exima laser emits light beam, and the emitted light beam is collimated to parallel light beam of a suitable size by a light beam transformer 42. The transformed light beam is homogenized by a homogenizer 43 comprising an array of a number of small lenses. An array of secondary light sources 44 is formed in a plane after the light beam is transmitted through the homogenizer 43, a secondary light source being formed at a focal point of each small lense.
A reticle 46 is illuminated by homogenized light beam through an illumination lense 45. Light beam transmitted through the reticle 44 is focused on an wafer 48 by a focusing lense 47.
Uniformly illuminated image of the reticle 46 is formed on the wafer 48 in a reduced dimension, and images of secondary light sources 44 are focused near an iris of the focusing lense 47.
This type of homogenizer 43 is used in an invention published on Japanese Patent Publication No. 13686/92. In a Japanese Patent Application which was laid open under Provisional Publication No. 147708/83, a pair of homogenizers(called integrator) are arranged in tandem in a light path so as to compensate non-homogeneity remained in a preceding homogenizer by a succeeding homogenizer.
In a Japanese Patent Application which was laid open under Provisional Publication No. 319727/89, and in a Japanese Patent Application which was laid open under Provisional Publication No. 166783/90, a light beam is divided into two parts by a half mirror, and one part of the divided light beam is inverted in position by a combination of prisms and lenses to be combined to the other part of the divided light beam for compensating non-homogeneity in the original light beam.
And in a Japanese Utility Application which was laid open under Provisional Utility Publication No. 124212/88, a homogenizer is composed of a matrix of optical fibers.
As described, homogenizers of prior art comprises lenses, prisms or optical fibers, and have a fairy long light path in glass material. When a light source of a short wavelength, such as an ArF exima laser light source, is used for the purpose of obtaining high resolution, light energy absorbed in the glass material will become large and loss of light intensity will become appreciable. And the glass material in a homogenizer might be damaged by heat generated from loss in the glass material.